1. Field of the Invention
The present invention relates to antenna devices preferably for use in near field communication (NFC) systems and other suitable systems, and to communication apparatuses including such antenna devices.
2. Description of the Related Art
International Publication No. 2013/183552 discloses an antenna device including a power feed coil to be connected to a power feed circuit and a booster coil antenna coupled with the power feed coil. The power feed coil described in International Publication No. 2013/183552 includes a first coil antenna and a second coil antenna. The first coil antenna and the second coil antenna are arranged in such a way that the winding axis direction of the first coil antenna is perpendicular to the winding axis direction of the booster coil antenna, whereas the winding axis of the second coil antenna is parallel to the winding axis of the booster coil antenna.
In the antenna device described in International Publication No. 2013/183552, both of the first coil antenna and the second coil antenna are coupled to the booster coil antenna only by magnetic fields around vicinities of corners of the booster coil antenna. Accordingly, the coupling strength between the power feed coil and the booster coil antenna (coil antenna) is weak.